Chemokines are chemotactic cytokines that are released by a wide variety of cells to attract macrophages, T cells, eosinophils, basophils and neutrophils to sites of inflammation (reviewed in Schall, Cytokine, 3:165-183 (1991), Schall, et al., Curr Opin. Immunol. 6:865-873 (1994) and Murphy, Rev. Immun., 12:593-633 (1994)). In addition to stimulating chemotaxis, other changes can be selectively induced by chemokines in responsive cells, including changes in cell shape, transient rises in the concentration of intracellular free calcium ions ([Ca2+]), granule exocytosis, integrin upregulation, formation of bioactive lipids (e.g., leukotrienes) and respiratory burst, associated with leukocyte activation. Thus, the chemokines are early triggers of the inflammatory response, causing inflammatory mediator release, chemotaxis and extravasation to sites of infection or inflammation.
There are two main classes of chemokines, CXC (alpha) and CC (beta), depending on whether the first two cysteines are separated by a single amino acid (C-X-C) or are adjacent (C-C). The alpha-chemokines, such as interleukin-8 (IL-8), neutrophil-activating protein-2 (NAP-2) and melanoma growth stimulatory activity protein (MGSA) are chemotactic primarily for neutrophils, whereas beta-chemokines, such as RANTES, MIP-1a, MIP-1b, monocyte chemotactic protein-1 (MCP-1), MCP-2, MCP-3 and eotaxin are chemotactic for macrophages, T-cells, eosinophils and basophils (Deng, et al., Nature, 381:661-666 (1996)). The chemokines bind specific cell-surface receptors belonging to the family of G-protein-coupled seven-transmembrane-domain proteins (reviewed in Horuk, Trends Pharm. Sci., 15:159-165 (1994)) which are termed “chemokine receptors.”
On binding their cognate ligands, chemokine receptors transduce an intracellular signal though the associated trimeric G protein, resulting in a rapid increase in intracellular calcium concentration. There are at least eleven human chemokine receptors that bind or respond to beta-chemokines and at least seven human chemokine receptors that bind to the alpha chemokines. Additionally CX3CR1 (fractalkine receptor) can bind to the fractalkine chemokine, which is distinguished by a series of three amino acids between the first two cysteines. Chemokine receptors, have been implicated as being important mediators of inflammatory and immunoregulatory disorders and diseases, including asthma and allergic diseases, as well as autoimmune pathologies such as rheumatoid arthritis and atherosclerosis.
CCR6 is known to be expressed primarily in B cells, IL17 secreting T cells, regulatory T cells and dendritic cells and shows strong binding to its cognate ligand CCL20 (MIP-3α). It is expressed on approximately 30-60% of adult peripheral blood effector/memory CD4+ T cells. CCR6 is involved in leukocyte homing to inflamed tissue, particularly the skin and lungs and is co-expressed on almost all T cells that have a skin homing phenotype, the CLA+ T cells. Thus CCR6 may be an important player in skin pathologies in which leukocytes participate.
CCR6 expression has been linked to psoriasis in the following manner. In humans, a large majority of skin-homing CD4 T cells in the peripheral blood express CCR6 with a greater degree of CCL20-mediated chemotaxis occurring in T cells isolated from psoriatic patients (Homey, et. al., JI, 2000). IL17 secreting cells are central agents in several inflammatory diseases. T cells, such as γδ T cells and TH17 T cells produce IL17 after activation. The pathogenic effects of IL17 have been associated with human diseases such as rheumatoid arthritis (Patel D D et. al., Ann Rheum Dis 2013), multiple sclerosis (Zepp J, Wu L, and X Li Trends Immunol 2011), and psoriasis (Martin D A et. al., J Invest Dermatol 2012). Evidence strongly linking IL17 with psoriasis include gene wide association studies that show strong association between psoriasis and genes upstream (IL-23) or downstream (NFκb) of IL17 signaling pathways as well as efficacy in targeting IL17 in a clinical setting (Martin D A et. al., J. Invest Dermat. 2012; Papp et. al., NEJM, 2012; Papp et. al., NEJM, 2012). In addition to enhanced CCL20-mediated chemotaxis, CCR6+ T cells isolated from psoriatic patients preferentially secrete IL-17A, IL22, and TNFα when compared to healthy controls (Kagami, et. al., J. Invest. Dermatol., 2010). Lastly, ccl20 mRNA was up-regulated in lesional psoriatic skin samples (Homey, et. al., JI, 2000; Dieu-Nosjean, et. al., JEM, 2000). In mice, CCR6 knock-out mice were protected from IL-23 driven psoriasis. Thus, a multitude of evidence in both mice and men suggest a protective role for CCR6 blockade in psoriasis and psoriasis-like models.
In view of the clinical importance of CCR6, the identification of compounds that modulate CCR6 function represent an attractive avenue into the development of new therapeutic agents. Such compounds and methods for their use are provided herein.